With the advance of miniaturization or the increase of operation speed of electronic equipment, high density packaging or high speed operation of electronic circuits to be mounted on the electronic equipment has been promoted to meet the situation. Since electronic parts constituting the electronic circuits are less spaced to each other in the high density packaging, particularly with the circuit of high operative frequency, error motion of the electronic circuit due to the unwanted radiation generated from each of electronic parts becomes a subject of discussion. In order to protect the electronic circuit from the unwanted radiation or to reduce the unwanted radiation which may affects the circuit, it is required to provide measures for shielding the circuit from electromagnetic waves. Also, since power consumption generally increases in high speed operation resulting In increase of the heating value of electronic parts, packaging of the electronic parts is required to have a good heat dispersion property.
The present inventor et al. have disclosed an electronic circuit package, in the Japanese Patent Laid-open Hei4-6893 (JP, A, 4-6893) Gazette, which allows high density packaging comprising a shielding characteristic for the electromagnetic waves while having a good heat dispersion property. This electronic circuit package is made of the metal base substrate through bending or drawing operation into a soup saucer shape. By disposing the electronic circuit package on another wiring substrate with its metal base substrate side up and the opening side down in order to Joint the opening side with the wiring substrate, the unwanted radiation to be leaked from the inside of the electronic circuit package is reduced while facilitating easy dispersion of heat. Since the electronic circuit package consists of only a single layer wiring conductor formed on the metal board having an insulation layer therebetween, It is unable to sufficiently meet the case in which multiple electronic parts are mounted with requirement of high density wiring. Since it is a metal base substrate, it cannot be expected to produce a multilayer substrate by merely using the through-hole plating technique. In addition, since this electronic circuit package is formed by shallow drawing, its external size tends to become much larger when compared with its effective inside measurement. Because of this, the electronic circuit package requires an extra space when it is mounted on the other substrate thereby making it difficult to realize high density packaging.
A QFP (Quad Flat Package), DIP (Dual Inline Package) or the like has been previously known as the representative package on which electronic parts are mounted. Lead frames are used as chip carriers to be used in these packages. Recently, applicable multiple-pin type electronic parts have increased in number, and lead frames for mounting these multiple-pin type electronic parts are required to have inner and outer leads with narrower pitch distances. While, since the outer leads are formed separately outwardly projecting from the package, It is difficult to narrow the pitch distance less than some extent in order to maintain the positional precision in packaging. As to inner leads, it is also difficult to form with certainty the portion which is adjacent to each of the electronic parts when the pitch distance is too narrowed. Therefore, it is estimated difficult to produce the package of the size smaller than the present one.
In order to meet these problems which are caused when lead frames are used, Japanese Patent Laid-open Hei1-132147 (JP, A, 1-132147) Gazette filed by Fujitsu (U.S. Pat. No. 4,953,173 Specification) discloses the package in which aluminum or copper is used as a base metal, a resin layer consisting of epoxy resin of several tens of micro meter thick is provided thereon as an insulation layer, subsequently copper foil is laminated, and after patterning thereof, a bend is formed by pressing. This package has electronic parts mounted on the center portion thereof using Its periphery as the outer leads. By composing the package in this way, it becomes possible to produce a minutely structured lead portion while keeping stability and at the same time it becomes possible to improve the heat dispersion property. However, this package uses epoxy resin as an insulation layer, and hence its thermal resistance is not sufficient. Also, since expansion coefficient of epoxy resin is small, when it is processed by deep drawing or bent with a small radius of curvature by means of pressing work, the insulation layer tends to generate cracks therein and exfoliate from the metal of the substrate, proving that it is not sufficiently reliable. After all, processing of this package by deep drawing is basically difficult, and its external size becomes relatively larger compared with the effective internal measurement of the package. Due to the above, this package requires an extra space when it is mounted on other substrates and has thus proved not to be sufficiently usable in high density packaging.
Further, Japanese Patent Publication Hei1-43473 (JP, B2, 1-43473) Gazette filed by Nukui et al. discloses the wiring substrate for mounting electronic parts using a metal board as a support substrate which has a thin metal film formed thereon by means of an ionic engineering deposition method. The support substrate, the organic insulation layer and the thin metal film of the wiring substrate are bent together into a product of a desired form. However, since the conductor layer of this wiring substrate is formed by the ionic engineering method, particular equipment for the process such as sputtering or vacuum evaporation is required, thus posing a problem that the production of the wiring substrate by this method is not easy.